Method for manufacturing coal agglomerates for use in direct iron smelting reducing furnace

ABSTRACT

A method for manufacturing coal agglomerates for use in a direct smelting reducing furnace is disclosed, in which a fine coal is agglomerated at a high temperature in a simple manner, or anthracite or low free swelling coal having a low free swelling index is mixed with the fine coal, and the mixture is agglomerated at a high temperature, thereby turning the low quality coal to useful purpose. The present invention is characterized in that a fine coal having a free swelling index of 3.0 or more and a particle size of 8 mm or less, or the fine coal mixed with 70 weight % of anthracite or a low free swelling coal, is maintained at 600° C. or over for 5 minutes or more, thereby manufacturing coal agglomerates for use in a direct smelting reducing furnace.

This application is a 371 of PCT/KR96/50251

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing coalagglomerates for use in a direct iron smelting reducing furnace. Morespecifically, the present invention relates to a method formanufacturing coal agglomerates, in which fine coal is agglomerated at ahigh temperature.

DESCRIPTION OF THE PRIOR ART

The coal which is used in a direct smelting reducing furnace as anenergy source has to have a uniform particle size (8-35 mm).

However, 50% or more of the coal which is supplied for use in the directsmelting reducing furnace is fine coal having a particle size of 8 mm orless. This fine coal is flown into the generator gas line when it is putinto the smelting furnace, and therefore, the fine coal becomes useless.

That is, the supplied ordinary coal is subjected to a particle sizeclassification, and the agglomerates having a size of 8 mm or more areput into the smelting reducing furnace after dewatering them. However,the fine coal having a particle size of 8 mm or less cannot be used.

Therefore, if the fine coal having a particle size of 8 mm or less is tobe used in the smelting reducing process, it has to be firstagglomerated.

A method of agglomerating the fine coal is disclosed in U.S. Pat. No.3,869,350 which relates to a method for heat-treating a coking coal. Inthis method, the fine coal is injected into a tube in which a hightemperature gas flows, thereby agglomerating the fine coal.

However, in the above described agglomerating method, there is thedisadvantage that a high temperature gas supply device is required, thetemperature rising rate having to be 100° C./sec.

SUMMARY OF THE INVENTION

In order to solve the above described problem, the present inventorcarried out research and experiments, and based on the result of theresearch and experiments, the present invention is proposed.

Therefore it is an object of the present invention to provide a methodfor manufacturing coal agglomerates for use in a direct smeltingreducing furnace, in which the self agglomerating trend of coal owing toits self sticking property during a thermal decomposition process isutilized, so that the fine coal can be agglomerated at a hightemperature in a simple manner.

It is another object of the present invention to provide a method formanufacturing coal agglomerates for use in a direct smelting reducingfurnace, in which anthracite or low free swelling coal having a low freeswelling index is mixed with the fine coal, and the mixture isagglomerated at a high temperature, thereby turning the low quality coalto useful purpose.

In achieving the above objects, the method for manufacturing coalagglomerates for use in a direct smelting reducing furnace according tothe present invention is characterized in that a fine coal having a freeswelling index of 3.0 or more and a particle size of 8 mm or less ismaintained at 600° C. or over for 5 minutes or more, therebymanufacturing coal agglomerates for use in a direct smelting reducingfurnace.

In another aspect of the present invention, the method for manufacturingcoal agglomerates for use in a direct smelting reducing furnaceaccording to the present invention is characterized in that a fine coalhaving a free swelling index of 3.0 or more and a particle size of 8 mmor less is mixed with 70 weight % of anthracite or allow free swellingcoal, and is maintained at 600° C. or over for 5 minutes or more,thereby manufacturing coal agglomerates for use in a direct smeltingreducing furnace.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object and other advantages of the present invention willbecome more apparent by describing in detail the preferred embodiment ofthe present invention with reference to the attached drawings in which:

FIG. 1 is a graphical illustration showing the variation of thecompressive strength versus the maintaining time during theagglomeration of the fine coal;

FIG. 2 is a graphical illustration showing the variation of thecompressive strength versus the maintaining temperature during theagglomeration of the fine coal; and

FIG. 3 is a graphical illustration showing the variation of thecompressive strength versus the mixing ratio between the anthracite andthe fine coal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The coal which is preferably used in agglomerating the fine coalaccording to the present invention is ordinary coal having a particlesize of 8 mm or less, and a free swelling index of 3.0 or more.

The above defined ordinary coal is obtained from a direct smeltingreducing process.

If the coal agglomerates for use in a direct iron smelting reducingfurnace are to be manufactured according to the present invention, thefine coal has to be maintained at 600° C. for 5 minutes or more. Thereason is as follows. If the maintaining temperature (agglomeratingtemperature) is below 600° C., the coal agglomerates are easily broken,and the compressive strength required in the direct smelting reducingfurnace cannot be obtained.

The higher the agglomerating temperature is, the more the compressivestrength is increased. Particularly, a superior compressive strength isobtained at a temperature of 650-800° C.

Therefore, if a superior compressive strength is to be obtained, amaintaining temperature of 650-800° C. should be preferably applied.

Further, during the agglomeration of the fine coal, the maintaining time(agglomerating time) has to be 5 minutes or more, and the reason is asfollows. If it is maintained for less than 5 minutes, the compressivestrength is lowered.

Meanwhile, the coal agglomerates can also be manufactured in such amanner that the fine coal is mixed with a low free swelling coal havinga low sticking property or with anthracite having no sticking property,and the mixture is maintained at 600° C. or over for 5 minutes or more.

The mixing proportion of the low free swelling coal or the anthracitehas to be 70 weight %, and the reason is as follows. If the proportionis more than 70%, the compressive strength which is suitable for thedirect smelting reducing furnace cannot be obtained.

Thus the fine coal is agglomerated according to the present invention,thereby producing coal agglomerates having a particle size of 8 mm ormore.

Here the coal agglomerates refer to that which is obtained from the finecoal through agglomeration.

In the present invention, a waste heat generated from the smeltingreducing furnace is used as the heat source. The fine coal is preferablyobtained from the direct iron smelting reducing process, and themanufactured coal agglomerates are for use in the direct smeltingreducing furnace.

Generally, the reducing gas which is generated from a smelting reducingfurnace has a temperature of about 1100° C. The optimum temperaturewhich is required by an upper shaft furnace is about 850° C. Therefore,prior to entering into the shaft furnace, about 20% of the reducing gasof about 850° C. is cooled down to about 50° C. during the passagethrough a ventury scrubber. This recycled cooled gas is flown into thegenerator gas line, so as to be used as a temperature control means forthe reducing gas.

Therefore, the high temperature fine coal agglomerating facility isinstalled upstream of the ventury scrubber. Thus, by utilizing the wasteheat of the high temperature (about 850° C.) reducing gas, the fine coalis agglomerated according to the present invention.

Further, the high temperature coal agglomerates which are obtained inthe above described method can be put into the top of the direct ironore smelting reducing furnace.

Thus the coal agglomerates for use in the direct smelting reducingfurnace are manufactured by utilizing the waste heat generated in thesmelting reducing furnace as the heat source, and by utilizing the finecoal obtained from the direct iron ore smelting reducing furnace. Inthis case, there are the following advantages.

That is, the fine coal of less than 8 mm obtained from the directsmelting reducing furnace can be turned to a useful purpose. The finecoal can be agglomerated by mixing it with the low free swelling coal orwith anthracite. Further, not only the waste heat of the reducing gascan be utilized to a useful purpose, but also the coal agglomerateswhich are heated to a high temperature (about 600° C. or over) can bedirectly put into the top of the direct iron ore smelting reducingfurnace. Therefore, the temperature raising heat which is required inthe case of using a normal temperature coal can be saved.

Now the present invention will be described based on actual examples.

Example 1

Two kinds of fine coals S. B. W. (south black water) coal and M.T.(mountain thorey) coal! which were obtained from a direct iron oresmelting reducing process and which had a free swelling index of 4.5 anda particle size of 8 mm were put into crucibles. Then these crucibleswere put into an electric furnace which had been heated to a temperatureof 850° C. Then their compressive strengths were measured at everymaintaining interval of 5 minutes up to 30 minutes. The measured resultsare shown in FIG. 1. As shown in FIG. 1, if the maintaining interval ismore than 5 minutes, a sufficient compressive strength can be obtained.That is, there was obtained a compressive strength of more than 5Kg/cm²which is the minimum compressive strength usable in the direct iron oresmelting reducing process.

Example 2

The M.T. coal of Example 1 was used with a maintaining interval of 10minutes, and by varying the maintaining temperature (reactiontemperature) by 50° C. up to 600-850° C., thereby agglomerating thecoal. Then the compressive strength was measured at the end of everytemperature interval of 50° C., and the measured results are shown inFIG. 2.

As shown in FIG. 2., when the maintaining temperature was 600° C., asufficient compressive strength could be obtained.

Example 3

The M.T. coal of Example 1 was heated in such a manner that the reactiontemperature was fixed to 850° C., and the reaction interval was fixed to10 minutes. Further, anthracite was mixed increasingly by 10% startingfrom 20% to 70%, thereby agglomerating the mixture coal. Thus thecompressive strength was measured at every 10% increase of anthracite,and the measured results are shown in FIG. 3.

As shown in FIG. 3, as the mixing amount of anthracite was increased, somuch the compressive strength was decreased, but up to 70%, thecompressive strength was sufficient for use in the iron ore smeltingreducing process.

According to the present invention as described above, the fine coalwhich is obtained from the direct iron ore smelting reducing process canbe agglomerated in a simple manner. Further, the anthracite having nosticking property or low free swelling coal can be mixed with the finecoal, and therefore, the energy utilization is done in an advantageousmanner. Particularly, in the case where a fine coal of 8 mm or lessobtained from the direct smelting reducing process is agglomerated basedon the present invention, the anthracite or the low free swelling coalhaving a low free swelling index can be utilized, thereby making itpossible to use even low quality coals. Further, the coal which isheated to a high temperature is put into the top of the direct iron oresmelting reducing furnace, and therefore, the dome shaped portion isnaturally heated, with the result that the energy can be saved.

What is claimed is:
 1. A method for manufacturing coal agglomerates for use in a direct iron ore smelting reducing furnace by using a fine coal, comprising the steps of:providing a fine coal having a free swelling index of 3.0 or more and a particle size of 8 mm or less, and agglomerating said fine coal by heating to a temperature of at least 600° C. for at least 5 minutes.
 2. The method as claimed in claim 1, wherein said fine coal is agglomerated at a temperature of 650-850° C.
 3. The method as claimed in claim 1, wherein said fine coal is obtained from a direct iron ore smelting reducing process.
 4. A method for manufacturing coal agglomerates for use in a direct iron ore smelting reducing furnace by using a fine coal, comprising the steps of:providing a fine coal having a free swelling index of 3.0 or more and a particle size of 8 mm or less, mixing said fine coal with one of a low free swelling coal or anthracite coal in an amount of no greater than 70 weight %, and agglomerating said fine coal mixture by heating to a temperature of at least 600° C. for at least 5 minutes.
 5. The method as claimed in claim 4, wherein said fine coal is agglomerated at a temperature of 650-850° C.
 6. The method as claimed in claim 4, wherein said fine coal is obtained from a direct iron ore smelting reducing process.
 7. The method as claimed in claim 2, wherein said fine coal is obtained from a direct iron ore smelting reducing process.
 8. The method as claimed in claim 5, wherein said fine coal is obtained from a direct iron ore smelting reducing process. 